When (compressed) gases such as compressed air are being employed, it is often required or at least desirable to remove condensable components from the gas. A method for this purpose known in the prior art is so-called refrigerant drying, i.e. the cooling of the gas to a lower temperature using refrigerant circulation and precipitating the condensed components. In this case, an additional counter-flow heat exchanger is provided by means of which the entering gas to be dried can be cooled by the cold exiting gas so that the required cooling capacity, on the one hand, and the relative moisture of the exiting gas, on the other, can be reduced.
Due to external conditions such as different temperatures of use and/or different incoming volume flows, a cooling capacity necessary for the cooling is often subjected to strong fluctuations. The cooling capacity needs to be adapted to such fluctuations, since too strong a cooling can lead to a solidification of the condensable components which can result in the plugging and/or damaging of the heat exchanger.
In terms of control technology, the capacity can be adapted by switching off a refrigerant compressor at a lower temperature limit and switching it on again at an upper temperature limit and/or after a determined time (ON/OFF control). With such a method, however, comparably larger fluctuations in the cooled air temperature curve and hence comparably larger fluctuations in the achievable pressure dew point will still arise.
An ON/OFF control with comparably low pressure dew point fluctuations is described in the prior art, namely EP 0 405 613 B1. In this case, the cooling capacity generated in excess when the refrigerant is circulated is effectively stored and output again to the gas to be cooled when refrigerant circulation is at standstill. The heat exchanger known in the prior art comprises quartz sand as the thermal mass between the refrigerant fluid and the air flow to be dried. The known heat exchanger enables operation at comparably low pressure dew point fluctuations but requires a considerable structural volume so as to realize the required exchange surfaces. Associated hereto is a high material expenditure of comparably expensive materials as well as a high weight of the heat exchanger and the accumulator material. Due to this, the dryer is relatively expensive, heavy and needs a larger floor space than a standard dryer.
DE 199 43 109 C1 proposes another solution with respect to the problem of pressure dew point fluctuations. According to DE 199 43 109 C1, a “standard heat exchanger” is proposed in conjunction with a circulating refrigerant fluid which is in turn cooled by refrigerant circulation. An ice-water mixture is generated by the refrigerant circuit. Storage takes place within the refrigerant fluid. In this context, as well, the constructional expenditure is not negligible due to the required second heat exchanger and a pump for pumping the ice-water mixture. Moreover, energy efficiency is reduced by the multiple heat transitions and the use of the pump. On the one hand, the pump needs electric drive power and, on the other, the heat input into the refrigerant fluid increases the required cooling capacity and consequently the power consumption of the refrigerant compressor.
U.S. Pat. No. 7,134,483 B2 proposes a latent heat storage material to be provided in a plate, with the plate contacting both a refrigerant plate and an air plate. In constructional respect, however, many questions remain unanswered. The U.S. Pat. No. 7,134,483 B2 document does not contain a specific description of how to configure the plates. As a whole, the configuration according to U.S. Pat. No. 7,134,483 B2 also seems to be comparably inefficient.
DE 103 11 602 A1 proposes a thermal accumulator to be provided in an edge area of a gas-refrigerant area of a heat exchanger. Providing the thermal accumulator at the outer sides of the heat exchanger, however, is comparably space-consuming and results in the heat exchanger operating at low energy efficiency.